1. Field of the Invention
The present invention relates to a switch module and a front-end module preferably for use in wireless communication, and to a driving method for the switch module.
2. Description of the Related Art
In order to support the international roaming services and to improve the communication speed, there is an increasing demand for multiband- and multimode-support cellular phones in which a single cellular phone terminal is capable of handling multiple frequency bands and multiple wireless systems.
Japanese Unexamined Patent Application Publication No. 2014-17750 discloses a carrier aggregation (CA)-support front-end circuit. This front-end circuit includes a 1-input n-output sPnT (single-Pole n-Throw) switch which connects a single common terminal with two or more selection terminals at the same time, a variable impedance adjusting circuit connected to a stage subsequent to the sPnT switch, and a duplexer connected to a stage subsequent to the variable impedance adjusting circuit. Japanese Unexamined Patent Application Publication No. 2014-17750 describes that, with the configuration of this front-end circuit, even if different frequency bands are used at the same time, a leakage of a signal into another circuit can be prevented.
However, in order to respond to all sorts of communication environments including multiband and multimode environments, it is necessary to consider, not only the communication quality of CA mode communication, but also that of single-band or single-mode communication, that is, so-called non-CA mode communication. In the front-end circuit disclosed in Japanese Unexamined Patent Application Publication No. 2014-17750, impedance adjustment is made to two frequency bands used at the same time in the CA mode, but impedance adjustment is not performed when the non-CA mode is used. That is, neither of impedance adjustment to a signal path for the non-CA mode while the front-end circuit is being operated in the CA mode nor impedance adjustment to a signal path for the CA mode while the front-end circuit is being operated in the non-CA mode is performed. In a CA-support front-end circuit, such as that disclosed in Japanese Unexamined Patent Application Publication No. 2014-17750, plural signal paths are connected to a switch. Accordingly, particularly when the front-end circuit is operated in the non-CA mode, impedance mismatching is likely to occur due to parasitic components generated within the switch, which leads to an increase in the signal loss. As a result, the bandpass characteristic is decreased.